The present invention relates to optical information recording systems. In particular, the present invention has application for optical recording systems for both reading and writing data. The invention relates to radial position detection of the read/write head in order to keep the head properly positioned over an information track on a recording media disk. In particular, such a recording media disk may be preformatted with clock information for use during the writing of information and the clock information may be sufficient to maintain the write/read head properly positioned over the preformatted track during the writing operation.
U.S. Pat. No. 4,063,287 relates to optical recording and shows an oscillating tracking mirror device for oscillating the radiation beam transversely with respect to the information track on an optical media disk. By scanning the information track transversely using the oscillating mirror, the information track may be followed using the tracking mirror device in order to maintain proper position of the information track with respect to the reflected beam detecting system. The patent does not show operation in the radial direction of the read/write head using the information generated using the oscillating tracking mirror device. The system according to the patent shows only the generation of a single radiation beam to be reflected from the optical media disk to provide tracking information as well as the other information derived from the reflected beam.
Also known to applicant is a United Kingdom published patent application, Publication No. GB 2 016 747 which shows an optical recording system having both reading and writing abilities in which a tracking system is provided for positioning the read/write head. In particular, the system shown in the publication relates to the use of an optical media disk which has a prewritten servo track. In one embodiment of that disclosure shown in FIGS. 6 and 7, a diffraction grating is used to generate a zero order beam together with plus one and minus one order beams which lie tangentially on the servo track ahead of and behind the zero order radiation beam, respectively. The diffraction grating in that disclosure is positioned so that the plus one order beam is positioned to one side of the center of the servo track and the minus one order beam is positioned to the opposite side of the center of the radiation track, leaving the zero order beam centered on the servo track.
Should the radial position alignment of the read/write beam change with respect to the servo track, a detector control system using the plus one and minus one order beams is used to adjust the radial position of the read/write beam in order to maintain servo track centering. Because the plus one and minus one order beams are in a fixed position with respect to the center of the servo track and because there is a time difference between the signals detected by the leading plus one order beam and the minus one order beam with respect to the same location on the information disk, the responsiveness of the system shown in the publication is not optimum for all tracking conditions.